1. Technical Field
The present invention relates to a piezoelectric device that is provided with a first substrate on which a first electrode layer is formed, and a second substrate on which a second electrode layer that is electrically connected to the first electrode layer, is formed, a liquid ejecting head and a method for manufacturing a piezoelectric device.
2. Related Art
Piezoelectric devices are provided with piezoelectric elements, and are applied to various liquid ejecting apparatuses, vibration sensors, and the like. For example, in liquid ejecting apparatuses, various liquids are ejected (discharged) from a liquid ejecting head using piezoelectric devices. Image recording apparatuses such as ink jet printers and ink jet plotters are examples of such liquid ejecting apparatuses, but in recent years, liquid ejecting apparatuses have been applied to various manufacturing apparatuses to make use of the feature of being able to accurately land a very small quantity of liquid in a predetermined position. For example, liquid ejecting apparatuses have been applied to display manufacturing apparatuses that manufacture color filters for liquid crystal displays, electrode formation apparatuses that form electrodes for organic Electro Luminescence (EL) displays and Field Emission Displays (FEDs), and chip manufacturing apparatuses that manufacture biochips (biochemical elements). Further, recording heads of image recording apparatuses eject liquid ink, and color material ejecting heads of display manufacturing apparatuses eject solutions of each color material of Red (R), Green (G), and blue (B). In addition, electrode material ejecting heads of electrode formation apparatuses eject materials of liquid electrode, and living organic material ejecting heads of chip manufacturing apparatuses eject solutions of living organic material.
The abovementioned liquid ejecting heads are formed by laminating a pressure-chamber-defining substrate that has a pressure chamber communicating with a nozzle, a piezoelectric element (a kind of actuator) that causes pressure fluctuations to be generated in liquid inside the pressure chamber, a sealing plate that is stacked over the piezoelectric element with a certain gap therebetween, and the like. Further, the above-mentioned piezoelectric element is driven by a driving signal that is supplied from a driving IC (also referred to as a driver IC). As an example of such a liquid ejecting head, International Publication No. 2012/176875 has disclosed a liquid ejecting head having a driving IC, a Tape Carrier Package (TCP) containing a driving IC, and the like. This driving IC, TCP, or the like is connected to an upper surface, which is opposite to a lower surface facing a piezoelectric element, and a driving signal from the driving IC is supplied to the piezoelectric element via wiring that is formed on the upper and lower surfaces of the sealing plate, penetration wiring that is formed inside a through hole in the sealing plate, and bumps that electrically connect a pressure-chamber-defining substrate and a sealing plate.
Solder bumps containing solder and metal bumps made from a metal (for example, gold or the like) are known as bumps that electrically connect two substrates. However, since it is difficult to suppress wet-spreading of the molten solder bumps, and thus it is difficult to form minute electrodes, solder bumps are not suitable for miniaturization of the liquid ejecting heads. Therefore, the use of metal bumps that can be formed in a semiconductor process (that is, a film formation process, a photolithography process, an etching process, or the like) without melting has been considered. However, since the rigidity of metal bumps is high, in order to electrically connect the metal bump reliably, the pressure applied to the substrates in a joining process becomes excessively high. Therefore, there is a concern that the substrates may be damaged. In particular, the sealing plate becomes vulnerable to breakage since the through holes for forming the penetration wiring is formed in the sealing plate.